The objective of this study is to provide neurochemical and neurophysiological data to determine if taurine functions as an inhibitory neurotransmitter released from stellate cells onto Purkinje cells in the cerebellar cortex. Neurochemical data will be obtained from normal rats and from rats which had their cerebella exposed to focussed low-level x-irradiation starting at different days after birth using schedules which prevent the acquisition of (a) late-forming granule cells; (b) stellate and granule cells; or (c) basket, stellate and granule cells. To determine if taurine may be present in stellate cells, frozen sections of normal and x-irradiated cerebella will be microdissected into the cerebellar cortex (containing the stellate, basket, Purkinje, Golgi and granule cells); white matter (containing the input and output fibers for the cerebellar cortex); and deep nuclei (groups of cells which send the signals out of the cerebellum). Ultracentrifugation techniques will be used to determine if taurine is present in nerve terminals isolated from the cerebella of normal and x-irradiated animals. If taurine is present in stellate cells then its levels should decrease in the cerebellar cortex and in nerve terminals of rats exposed to a schedule of x-irradiation which prevents the formation of stellate cells. In vitro release studies using cerebellar slices and isolated nerve endings will also be done on normal and x-irradiated rats. Elevated K ion and glutamate (in the presence and absence of Ca ions) will be used to stimulate the release of taurine. Neurophysiological studies will be done to determine if microiontophoretically applied taurine inhibits the firing of Purkinje cells.